In this study, effects of position, diameter (5, 6, 7, 8 mm) and angle (30 degrees-180 degrees) of a mobile plug, located at the hot outlet side in a Ranque-Hilsch Vortex Tube (RHVT), were determined experimentally for best performance. In addition to plug parameters, effects of supply pressure (200-420 kPa) and number of nozzles (2, 4, 6) were also studied. The internal diameter (D) of the vortex tube used in the experiments was 9 mm; the ratio of the length of the vortex tube to its diameter (L/D) was 15. Four different plug locations were studied. The maximum difference in the temperatures of hot and cold streams was obtained for the plug diameter of 5 mm, tip angles of 30 degrees and 60 degrees, 4 nozzles and by keeping the plug location at the far extreme end. (C) 2008 Elsevier Ltd and IIR. All rights reserved.